Portable dialysate supply system



April 28, 1970 E. J. SERFASS ET AL 3,508,656

PORTABLE DIALYSATE SUPPLY SYSTEM 2 Sheets-Sheet Filed April 10, 1968mohhzoi m I k (\1 United States Patent 3,508,656 PORTABLE DIALYSATESUPPLY SYSTEM Earl J. Serfass, St. Petersburg, and Vernon H. Troutner,Clearwater, Fla., assignors to Milton Roy Company, St. Petersburg, Fla,a corporation of Pennsylvania Filed Apr. 10, 1968, Ser. No. 720,104 Int.Cl. B01d 35/14, 35/00 US. Cl. 210-90 4 Claims ABSTRACT OF THE DISCLOSUREA portable blood dialysis system in which dialysate fluid is mixed andsupplied with a constant concentration is described. Water and dialysatefluid concentrate are mixed to form dialysate fluid which is supplied tothe dialyzer. The concentration of the dialysate fluid is continuouslymonitored by a conductivity cell. The output of the conductivity cell isapplied to control a pump which supplies the concentrate. This pump alsohas a secondary speed control loop. A tachometer in the secondary loopcorrects speed variations caused by changes other than the conductivitycell output signal.

BACKGROUND OF THE INVENTION One of the most successful means fortreating chronic kidney failure is by hemodialysis using an artificialkidney system. In hemodialysis the patients blood is circulated from anartery through an artificial kidney, or dialyzer, where excess water andwaste materials are removed. The blood is returned to the patientsveins.

A central station dialysate supply system for supplying dialysate fluidto a number of patients in a hospital is described in Transactions ofthe American Society of Artificial Organs, vol. X, 1964, page 107,Grimsrud, Cole, Lehman, Babb and Scribner.

Also, in the Austin et al. Patent 3,352,779 there is described a systemfor mixing dialysate fluid in large batches for supply to a number ofpatients.

Since the patient must undergo dialysis treatment several times a weekit is desirable that a system be provided which can be used by thepatient in his home. A single patient dialysate supply system withextensive monitoring controls which makes the system safe for use by thepatient himself is described in Controlled Blood Dialysis System, Ser.No. 563,523, now US. Patent No. 3,441,136, filed July 7, 1966, Earl J.Serfass, John E. Martin and William E. Wilson, Jr. Such a single patientsystem is also described in a paper presented before the InstrumentSociety of America, 22nd Annual ISA Conference and Exhibit, Sept. 11-l4,1967, by Dr. E. J. Serfass, Preprint Publication No. 26-1-BIOMED67.

These single patient systems have found widespread successful use.However, they do not meet all requirements of some patients because thesystems utilize expensive proportioning apparatus for mixing dialysatefluid and because the systems are quite large and not portable.

All of the blood dialysis supply systems described above use atwo-stroke pump to mix dialysate concentrate with water to produce asupply of dialysate fluid. These pumps have very accurate controlledstrokes so that the water and the concentrate are mixed in preciseVolumetric proportions. The pumps are relatively expensive and bulky.Further, extensive movement of the pump will affect the calibration sothey are not suitable for a truly portable system.

While these two-stroke pumps do mix concentrate and water in precisevolumetric proportions, the resulting dialysate fluid does notnecessarily have a controlled concentration. When the density of theconcentrate changes with temperature, the concentration of the dialysatefluid changes. What is required in dialysate supply systems is theproduction of a dialysate fluid having controlled sodium and chlorideconcentration at a prescribed temperature.

The variation of the concentration of the dialysate fluid with change intemperature is a particular problem in a system having extensive monitorcontrols such as the systems described in the above-mentioned Serfassreference and Serfass et al. patent application. These systems have aconcentration monitor which sounds an alarm when the concentration ofthe dialysate fluid varies outside of preset limits. When dialysistreatment is performed during the night, as it is frequently, thepatient will often be awakened by the alarm when the concentration ofthe dialysate fluid changes because of a change in the ambienttemperature of the top water.

SUMMARY OF THE INVENTION This invention relates to blood dialysis supplysystems and more particularly to a portable blood dialysis system.

In accordance with an important aspect of this invention, the dialysatefluid and tap water are mixed in a system which includes a servocontrolled pump. The servo controlled pump supplies concentrate to amixer. The water and concentrate are mixed to form dialysate fluidhaving a controlled concentration. A conductivity cell monitors theconcentration of the dialysate fluid and the resultant signal controlsthe pump. This permits the use of a relatively simple, compact,inexpensive pump in the system rather than more costly and bulkyvolumetric measuring devices.

Further in accordance with this invention, a secondary control loop isprovided for the pump by a tachometer control. When the speed of thepump varies because of variations other than conductivity, line voltage,for example, the tachometer senses these changes in the pump speed andquickly restores the pump to its normal operating speed.

Accordingly, it is an important object of the present invention toprovide a simple, easily maintained, inexpensive dialysate supplysystem.

It is another object of the present invention to provide a portabledialysate supply system which can be operated from a volt, 15 amperepower supply and an ordinary cold water supply.

The foregoing and other objects, features and advantages of theinvention will be better understood from the following more detaileddescription and appended claims together with the drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 shows a diagram of the portabledialysate supply system; and

FIG. 2 shows a schematic diagram of the control loops for theconcentrate pump.

DESCRIPTION OF A PARTICULAR EMBODIMENT Referring now to FIG. 1, theblock diagram shows the circulation of dialysate fluid and theelectrical control functions performed by the system. In FIG. 1 thehydraulic conections are shown with heavy lines while the electricalconnections are shown with lighter lines.

The dialysate fluid to be circulated in the dialyzer is a mixture of tapWater from the source 34 and concentrate from the concentrate reservoir15. The composition of the dialysate fluid may be changed in accordancewith the therapy required for a particular patient. In general, thecomposition of the dialysate fluid is described in Hemodialysis forChronic Renal Failure, Freeman, M'aher and Schreiner, Annals of InternalMedicine, volume 62, No. 3, March 1965. The concentrate and tap waterare mixed in the proper proportions in the mixer 11. Water from thesource 34 passes through the pressure reducing valve 2 to the air trapand vent 3. Overflow from the air trap and vent 3 goes to drain 35.

A flow control valve 4 provides the desired flow and flow meter 5monitors the flow of water. The water passes through the normally opensolenoid valve 6. During sterilization of the system the norm-ally openvalve 6 is closed and the manually operated by-pass valve 7 is preset toprovide about one-fourth the flow of water which is heated to a muchhigher temperature. Automatic reduction of water flow duringsterilization is an important feature resulting in reduction of heatersize, cost, and power requirements.

The water is supplied to an electric heater 8 which produces water atthe desired temperature, approximately 37 C. for normal dialysis andapproximately 95 C. for sterilization. Thermistor sensing circuitry 9 isprovided for controlling the heater 8, that is, varying the electriccurrent to obtain the desired heating. Thermistor circuitry 10 monitorsthe water temperature and actuates an alarm relay when the watertemperature is outside of normal limits.

A controllable volume pump 13 supplies dialysate concentrate from thereservoir 15 through the check valve 12 to the mixer 11.

The mixed water and concentrate passes through the concentration controlelement 18 on its way to the dialyzer. The concentration control element18 is a conductivity cell which produces an electrical signalrepresenting the concentration of the dialysate fluid supplied from themixer 11. The electrical signal produced by the conductivity cell isapplied to the pump 13 to control the volume of concentrate supplied tothe mixer 11 so that the concentration of the dialysate fluid remainsconstant. The control circuitry for this control loop is shown in blockform in FIG. 2. A secondary speed control loop is provided for the pump13. This control loop includes a tachometer 33 driven at the same speedas the pump 13. The tachometer 33 produces an electrical signalrepresenting the speed of the pump and this is applied to maintain thespeed of the pump constant regardless of variations other thanconductivity changes.

Another conductivity cell 19 is provided for monitoring the conductivityof the dialysate fluid. The dialysate fluid is supplied to the constanthead vessel 20. The head vessel 20 has an overflow outlet 21 coupledthrough a drain cup 24 to the gravity drain 35.

The head vessel 20 provides a supply of dialysate fluid at a constantpressure to the dialyzer. The dialysate fluid is supplied throughpressure control valve 25 to the inlet dialysate port of the dialyzerwhich may be of the Kiil type, for example. In this type of dialyzer,blood ports are provided for passage of blood on one side of a membraneand dialysate ports are provided for passage of dialysate fluid on theother side of the membrane. The dialysate fluid passes through thedialyzer on one side of the membrane and out through the outletdialysate port.

A pressure gauge 27 is provided to monitor the negative pressure at theoutlet of the dialyzer. Flow meter 28 is provided to monitor the flowrate through the dialyzer and blood leak detector 29 is provided tosense the presence of blood in the dialysate fluid.

A vacuum breaker 30 is provided so that if the system becomes clogged, alarge negative pressure which might break the membrane will not beapplied to the dialyzer. The eflluent pump 32 applies the negativepressure through check valve 31, and regulates dialysate flow throughthe dialyzer.

All of the monitors are connected to shut off the efiluent pump 32 andstop dialysate flow through the dialyzer when any of the monitoredconditions exceed the preset limits. The temperature monitor thermistorcircuit 10, the conductivity monitor 19, over-temperature sensor 23,pressure gauge 27, and blood leak detector 29 are all monitoringcircuits of the type in which a set of relay contacts are activated whenthe monitored condition exceeds its adjustable preset limits. All ofthese relay contacts are connected in a circuit to control the voltpower for the eflluent pump 32. When any monitored condition exceeds itslimits the relay contacts will be activated and power will be cut off tothe pump 32.

Also included in this control circuit is a level monitoring probe, 22,of the conductivity type located in the head vessel. If dialysatemake-up rate becomes less than the flow rate to the dialyzer, the leveldrop in the head vessel is sensed and the efiluent pump 32 turned ofi.

In addition to, or in place of, the concentration monitor 19, an Ag,AgCl detector may be provided. Such a detector would similarly beconnected to monitor the chloride content of the dialysate fluid andturn oil the pump 32 when the concentration is outside the desiredlimits. The silver, silver chloride detector could also be used in placeof concentration control element 18 to control the pump 13.

The system is electrically programmed to automatically proceed throughthe following steps; rinse, pre-sterilize, normalize, monitor test,alarm test, system test, dialyze, after-sterilize. The control systemand monitors are interlocked to prevent the flow of anything other thannormal dialysate to the dialyzer.

The system for controlling the pump 13 in accordance with the controlsignal from the concentration monitor can be of well known type. Onesuitable system is shown in block form in FIG. 2. The conductivity cellincludes a sensor 36 for determining conductivity. Another sensor 37which is temperature sensitive, provides temperature compensation forthe conductivity cell 36. The sensors 36 and 37 are connected in abridge circuit 38. Variations in the conductivity from a given setpointproduce an error signal which is amplified in amplifier 39. The phasedetector 40 senses the phase of the error signal which is an indicationof whether the conductivity is above or below the setpoint. The errorsignal is compared with an adjustable setpoint in the setpoint control41.

The error signal from the setpoint control 41 is compared with thesignal from tachometer 33 in the error comparator 42. The resultantsignal is amplified in error amplifier 43 and power amplifier 44 and isused to drive the servo motor 45. As is conventional, there is feedbackfrom the servo motor 45 to the error amplifier 43. The servo motor 45drives the concentrate pump 13 to provide the desired volume ofconcentrate to the mixing chamber 11.

What is claimed is:

1. A blood dialysis system comprising:

a dialyzer having a membrane, blood ports for passage of blood throughsaid dialyzer on one side of said membrane and dialysate ports forpassage of dialysate fluid through said dialyzer on the other side ofsaid membrane,

a source of dialysate concentrate,

a mixer for mixing said water and said dialysate concentrate to producedialysate fluid, said dialysate fluid being supplied from said mixer tosaid dialysate ports,

a controllable volume electrically driven pump connected to continuouslysupply dialysate concentrate from said source of concentrate to saidmixer,

a conductivity cell continuously producing an electrical signalrepresenting the concentration of the dialysate fluid supplied from saidmixer to said dialysate ports,

means for applying said electrical signal to said pump to control thevolume of concentrate supplied to said mixer so that the concentrationof said dialysate fluid remains constant,

a tachometer driven at the same speed as said pump, said tachometerproducing a tachometer signal representing the speed of said pump, and

means for applying said tachometer signal to maintain the speed of saidpump constant.

2. The system recited in claim 1 further comprising:

an eflluent pump for supplying said dialysate fluid from said mixer tosaid dialysate ports,

means for monitoring the conditions of the dialysate fluid, and

means responsive to said monitoring means for deenergizing said efliuentpump when any monitored condition exceeds preset limits.

3. The system recited in claim 2 wherein said monitoring means includes:

a temperature monitor,

a conductivity monitor,

a pressure gauge, and

a blood leak detector, each having a set of relay contacts which areactivated when the monitored condition exceeds preset limits, said relaycontacts being connected in a circuit to control the application ofpower to said eflluent pump.

4. A blood dialysis system comprising:

a dialyzer having a membrane, blood ports for passage of blood throughsaid dialyzer on one side of said membrane and dialysate ports forpassage of dialysate fluid through said dialyzer on the other side ofsaid membrane,

a source of water,

a source of dialysate concentrate,

a mixer for mixing said water and said dialysate concentrate to producedialysate fluid, said dialysate fluid being supplied from said mixer tosaid dialysate ports,

a controllable volume, constant speed, electrically driven pumpconnected to continuously supply dialysate concentrate from said sourceof concentrate to said mixer,

a conductivity cell continuously producing an electrical signalrepresenting the concentration of the dialysate fluid supplied from saidmixer to said dialysate ports,

a heater connected between said source of water and said mixer,

a normally open solenoid valve connected between said source of waterand said heater from supplying a normal flow of Water to said heaterduring dialysis, said normally open valve being closed duringsterilization of said system,

a bypass around said normally open valve, and

a bypass valve in said bypass, said bypass valve being preset to provideabout one-fourth said normal flow of water to said heater duringsterilization so that said water is heated to a much higher temperatureduring sterilization.

References Cited UNITED STATES PATENTS 3,352,779 11/1967 Austin et al.2l0-23 3,406,826 10/1968 Willock 210321 X 3,416,664 12/1968 Kumme et a1.210l03 X REUBEN FRIEDMAN, Primary Examiner F. A. SPEAR, JR., AssistantExaminer US. Cl. X.R.

gg ggg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,508,656 Dated 'Mhv 11. 1910 Inventor) EARL J. SERFASS and VERNON H.TROUTNER It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 16, change "top" to tap- Column 4 line 56, after"membrane," indent and insert -a source of water,-

SIGNED M521 SEALED (SEAL) mm: 1:. sum, an. Edward u M I! Gomisaiomr ofPatents Attestin Oifioar

